It has been found that lead acid secondary batteries with plates or electrodes, primarily positive plates or electrodes, made from tetrabasic lead sulfate give advantageous results in certain applications, such as standby service, where battery life should be measured in decades. It has also been found that the most efficient and commercially practical shape for such a battery, considering volumetric efficiency and cooling surface area, is a cylinder. A proposed commercial embodiment of such a battery is shown in U.S. Pat. No. 3,765,943, issued to Biagetti on Oct. 16, 1973, entitled "Fabrication of Lead-Acid Batteries", and U.S. Pat. No. 3,899,349, issued to Yarnell on Aug. 12, 1975, entitled "Carbon Dioxide Curing of Plates for Lead-Acid Batteries", both being hereby incorporated by reference. In these illustrations, and in the actual commercial embodiment of such a battery, the positive and negative plates or electrodes are vertically interleaved, with separators between the plates or electrodes, and with separate insulators on the outer periphery of the negative plate or electrode, and on the inner circumference of the positive plate or electrode. Positive plates are joined together at their outer periphery, and negative plates or electrodes are joined together at their inner circumference. In the actual commercial embodiment of such a battery, positive plates or electrodes are joined only intermittently at their outer peripheries, the unjoined portions requiring separate insulators.
The purpose of such insulators, and of such separators, is to prevent active material which may become separated from the remainder of the mass of the plate or electrode from falling away and forming electrical shorts between positive and negative plates or electrodes to protect the electrodes from the effects of any such material that may escape, and also to prevent the formation of long, fragile hairlike dendrite growth at the edge of plates, which may form a shorting path to an adjacent plate or break off to become part of a growing conductive mass on the floor of the battery.
The separators in commercial use are disks of microporous rubber and fiberglass matting. Each negative plate or electrode is manually fitted with insulation about its outer periphery in the form of a rubber channel having a generally U-shaped cross section which is cut to length and fitted over the edge of the plate. The positive plate or electrode is fitted with insulation at its inner periphery, the insulator being a rubber circular member having a periphery in the form of an outwardly-directed U-shaped channel, which is compressed and inserted into the central opening of a positive plate, to insulate the inner edge of the plate. Then, three pieces of U-shaped rubber channel are cut to length, and fitted over the outer edge of the positive plate between three portions left free of active material for joining positive plates together. Then, the positive and negative plates or electrodes are vertically stacked and interleaved, with separating disks of porous rubber and fiberglass matting.
As will be apparent, the manual handling needed to install the central insulator in the positive plate or electrodes, the three separate outer insulators on the positive plate or electrode, and the outer insulator on the negative plate or electrode, as well as manually placing the round rubber separators and fiberglass mats in place, is apt to cause damage to the plates or electrodes even when great care is used, and the handling involved creates an undesirable opportunity for exposure of the assembler to the danger of lead toxicity.
After the battery has been successfully assembled, the edge insulators offer only marginal protection against interplate shorts, due to unavoidable gaps in the insulators, and the overlap and short edge-to-edge distances between positive and negative plates or electrodes.
The instant invention provides a set of insulators which overcomes or greatly reduces the severity of these problems.